Involvement of the PPPGHR motif in T cell activation via CD2.

Prior studies identified a segment of the CD2 cytoplasmic domain between amino acid (aa) residues 253 and 287 as important in T lymphocyte signal transduction. This region contains two repeats of the sequence motif PPPGHR, thought to form a "cage" structure involved in CD2-mediated signaling. To evaluate this segment, a series of mutant human CD2 molecules were produced by oligonucleotide-directed mutagenesis and inserted into the ovalbumin-specific, I-Ad-restricted murine T-T hybridoma 3DO54.8 using the DOL retroviral system. CD2 M1 (271-272), CD2 M2 (278-279), and CD2 M4 (264-265) mutants replaced the positively charged adjacent aa histidine and arginine (HR) in the wild-type CD2 sequence with aspartic and glutamic acid (DE) at positions 271-272, 278-279, and 264-265, respectively. In addition, a truncation mutant, CD2 M3 (268), containing only 57 of the 117 cytoplasmic aa and terminating before the second PPPGHR sequence, was generated. Stimulation of transfectants CD2 FL, CD2 M1 (271-272), and CD2 M2 (278-279) with anti-T11(2) + anti-T11(3) antibodies resulted in a rise in cytosolic-free calcium [( Ca2+]i) and subsequent interleukin 2 (IL-2) secretion. In contrast, CD2 M4 (264-265) transfectants could not be activated in either assay. Thus, alteration of histidine 264 and/or arginine 265 within the first PPPGHR motif affects the process of signal transduction via CD2, whereas identical mutations in residues at 271-272 or 278-279 were individually without effect. Consistent with these data, CD2 M3 (268) transfectants were able to generate a detectable amount of IL-2 via CD2 triggering. These data support the notion that the PPPGHR motif at aa 260-265 is important for activation of T lymphocytes via the CD2 molecule.

Characterization of Fc epsilon RI gamma in human natural killer cells.

We report the characterization of the Fc epsilon RI gamma chain which associates with the transmembrane form of CD16 to form the low affinity receptor for IgG (Fc gamma RIII) expressed on human natural killer (NK) cells. cDNA cloning and sequence analysis of Fc epsilon RI gamma from a polyclonal CD3-CD16+ NK line established that this molecule is identical to Fc epsilon RI gamma previously identified in human basophils as part of a high affinity receptor for IgE. Polymerase chain reaction analysis of Fc epsilon RI gamma gene expression in a series of CD3+CD16- and CD3-CD16+ NK clones reveals that Fc epsilon RI gamma is not directly linked to NK activity since clones of the CD3+CD16- phenotype lack Fc epsilon RI gamma RNA but nevertheless mediate cytotoxicity. Taken together, these results demonstrate that the Fc epsilon RI gamma molecule is expressed in various types within the hematopoietic system as part of multimeric surface receptors involved in different biological functions.

Human natural killer cells and mature T lymphocytes express identical CD3 zeta subunits as defined by cDNA cloning and sequence analysis.

In order to characterize the CD3 zeta-related protein found in human natural killer (NK) cells and compare it with CD3 zeta expressed in T lymphocytes, the present study was performed. A polyclonal CD3-CD16+NK population displaying a strong non-major histocompatibility complex-restricted cytotoxic activity against the NK target K-562 was isolated and a product corresponding to CD3 zeta amplified using the polymerase chain reaction method. This 0.6-kb product was present in similar amounts in NK cells and T cells. In contrast, a product corresponding to CD3 delta was amplified from T lymphocytes exclusively. Thus, the CD3 zeta product detected in NK cells did not originate from contaminating T cells. DNA sequence analysis of two independent polymerase chain reaction products from the NK cells demonstrates that human NK cells and mature T cells share a CD3 zeta subunit with an identical primary amino acid sequence. The nucleotide sequence of a third NK-derived cDNA revealed an insertion of a CAG triplet encoding an additional glutamine residue in the cytoplasmic domain. Since this residue is encoded by nucleotides at a putative RNA splice junction, it possibly results from a difference in pre-mRNA splicing. Taken together, these data show that CD3 zeta is not structurally distinct in NK cells and in T lymphocytes.

A population of early fetal thymocytes expressing Fc gamma RII/III contains precursors of T lymphocytes and natural killer cells.

We have identified a dominant fetal thymocyte population at day 14.5 of gestation in the mouse that lacks CD4 and CD8 but expresses Fc gamma RII/III several days prior to acquisition of the T cell receptor (TCR) in vivo. If maintained in a thymic microenvironment, this population of CD4-CD8-TCR-Fc gamma RII/III+ thymocytes differentiates first into CD4+CD8+TCRlowFc gamma RII/III- thymocytes and subsequently CD4+CD8-TCRhighFc gamma RII/III- and CD4-CD8+TCRhighFc gamma RII/III- mature Ti alpha-beta lineage T cells. However, if removed from the thymus, the CD4-CD8-TCR-Fc gamma RII/III+ thymocyte population selectively generates functional natural killer (NK) cells in vivo as well as in vitro. These findings show that a cellular pool of Fc gamma RII/III+ precursors gives rise to T and NK lineages in a microenvironment-dependent manner. Moreover, they suggest a hitherto unrecognized role for Fc receptors on primitive T cells.

CD3 zeta dependence of the CD2 pathway of activation in T lymphocytes and natural killer cells.

In T lymphocytes, signal transduction through the CD2 adhesion molecule requires surface expression of the CD3-Ti T-cell receptor (TCR) complex. In contrast, in natural killer (NK) cells, CD2 functions in the absence of a TCR. Because the TCR on T lymphocytes and the CD16 low-affinity IgG Fc receptor (Fc gamma receptor type III) complex on NK cells share a common CD3 zeta subunit, we reasoned that CD3 zeta may be critical for CD2 signaling in T lymphocytes and NK cells. Here we show that transfection of a cDNA encoding a transmembrane form of CD16 into TCR- variants of the Jurkat T-cell line results in CD16 expression in association with endogenous CD3 zeta homodimers and restores CD2 signaling function. To test directly the role of CD3 zeta in CD2 triggering, we then transfected human CD2 into each of two murine T-T hybridomas that express TCRs containing either a full-length CD3 zeta subunit or a truncated CD3 zeta subunit incapable of transducing signals. Despite expression of equivalent surface levels of TCR, CD2-mediated signaling is seen only in the T cells containing wild-type CD3 zeta. These findings show that (i) CD16 on NK cells is functionally equivalent to the TCR on T lymphocytes for coupling CD2 to signaling pathways and (ii) CD2 signal transduction depends upon the CD3 zeta subunit of the TCR complex and, by inference, the CD3 zeta subunit of the CD16 complex.

Complementary roles for CD2 and LFA-1 adhesion pathways during T cell activation.

The influence of T cell receptor (TcR) triggering on T cell adhesion function has been systematically investigated in the present studies; we show that the adhesion function of LFA-1 is minimal in non-activated T cells but is augmented within minutes following TcR-mediated activation. In contrast, CD2 function is essentially optimal in non-activated T cells and undergoes no detectable modification within 12 h of TcR stimulation. Protein kinase C activation augments LFA-1 but not CD2 adhesion function and cyclic AMP reduces LFA-1 adhesion without affecting CD2-LFA-3 interactions. Up-regulation of the LFA-1 pathway occurs in the absence of any detectable surface redistribution of this molecule, suggesting an activation dependent modification leading to a high-affinity ICAM-1 binding state. The TcR independence of CD2 adhesion function implies a critical role of the CD2 pathway in initiating cell-cell interactions prior to TcR engagement and LFA-1-ICAM-1 binding and underscores the complementary nature of the CD2 and LFA-1 adhesion pathways during the immune response.

Practice guidelines for lipid-based amphotericin B in stem cell transplant recipients.

OBJECTIVE: To provide clinicians who practice in the stem cell transplantation (SCT) setting with practical guidelines for the use of lipid-based amphotericin B (AmB) formulations in SCT patients who have documented or probable invasive fungal infections, are experiencing neutropenic fever, or require secondary prophylaxis for fungal infections. DATA SOURCES: Recommendations are based on the results of a two-day consensus meeting that convened clinicians versed in the management of infectious complications in patients undergoing SCT. This meeting, which was held October 21-23, 1998, in Orlando, Florida, was sponsored by an educational grant from The Liposome Company. In addition, primary articles were identified by MEDLINE search (1980-December 1999) and through secondary sources. STUDY SELECTION AND DATA EXTRACTION: All of the articles identified from the data sources were evaluated, and all information deemed relevant was included in this review. DATA SYNTHESIS: Immunocompromised patients, particularly patients undergoing high-dose chemotherapy with SCT, experience a high degree of morbidity and mortality from invasive fungal infections. Historically, treatment for such infections with conventional AmB had been limited primarily by its associated nephrotoxicity. Lipid-based formulations of AmB have helped to advance the management of invasive fungal infections in the SCT population by offering a treatment alternative that allows for administration of adequate amounts of active drug to produce clinical and mycologic responses, compared with conventional AmB, in a delivery system that is less nephrotoxic. Unfortunately, these agents are relatively expensive. Therefore, patients who are candidates for lipid-based products must be selected carefully. CONCLUSIONS: Practical guidelines are provided for the use of lipid-based AmB formulations in SCT patients who have documented or probable invasive fungal infections, are experiencing neutropenic fever, or require secondary prophylaxis for fungal infections.